The weighing of individual food items transported along a conveyor is today an important operation in processing food items. If one had to weigh every item individually on a stationary weighing unit, the processing speed would be extremely low.
A belt weigher is an instrument used for weighing items while the items are being conveyed and is basically a conveyor with a built in weighing platform. Such belt weighers have been known for quite some time in the food processing industry. In the last years there has been some development is such belt weighers with the aim of providing a fast belt weighers with high accuracy. This is essential in the food processing to measure as exact as possible the weight of the object being processed prior to various types of operations such as sorting, cutting, or packaging.
One of the main problems that arises in such belt weighers, especially those available for the food processing industry is the fact that the tension, flexibility and the weight of the belt will affect the accuracy of the weighing. A stiff and heavy belt will degrade the accuracy more than a light and flexible belt. The tension of the belt has therefore a large influence on the accuracy of the weighing. A high tension causes a lower accuracy in weighing than a low tension of the belt. Accordingly, to maximize the accuracy of the belt weight it is best to use a belt that is light and flexible with as low tension as possible, but still high enough for the driving mechanism to move the conveyor belt while the driving sprocket that runs the belt must have a secure grip on the belt.
Another important issue in maintaining a high accuracy in the weighing is to prevent the belt from oscillating, where any oscillation of the belt will also affect the accuracy of the weighing process. Other parameters that affect the accuracy in the weighing are temperature fluctuations and wearing in the belt.
Through the temperature increase the length of the belt increases, which varies the tension in the belt and therefore the accuracy in the weighing, and vice verse, through a decrease in the temperature the length of the belt decreases and the tension increases.
The problem with the tension of the belt has partly been solved by using modular plastic belt and let it hang on the return-way on a few load-bearing rollers. This has the drawback that the belt can easily oscillate and therefore affect the weighing.
There is therefore a need for a belt weigher where the tension of the belt is maintained optimal and wherein the oscillation are reduced so that accuracy of the weighing may be increased.